Increasingly stringent environmental protection considerations have led to intensified efforts to reduce the sound level associated with devices such as small engine operated chain saws, vehicles, and tools of various nature.
In this connection, prior practioners in the muffler art have employed the technique of splitting an exhaust flow, with the split flow being subsequently merged, as evidenced by the disclosure of Martinez U.S. Pat. No. 4,165,798 (Aug. 28, 1979).
Other techniques for utilizing split flow arrangements in muffler structures are disclosed in patents such as:
Benez--U.S. Pat. No 3,177,973 (Apr. 13, 1965) PA1 Becker et al.--U.S. Pat. No. 3,704,763 (Dec. 5, 1971) PA1 Brown--U.S. Pat. No. 3,750,841 (Aug. 7, 1971) PA1 Bychinsky--U.S. Pat. No. 3,948,349 (Apr. 6, 1976) PA1 Gordon et al.--U.S. Pat. No. 3,968,854 (July 13, 1976) PA1 flowing gas from each of the first and second flow paths generally toward and into each other as mutually opposed gas flows to form a unified exhaust gas flow; and PA1 permitting increments of the exhaust gas flow to exit from the muffler means, sequentially along the flow of the exhaust gas flow.
It has also been recognized, for example in above noted Gordon et al. U.S. Pat. No. 3,968,854, that sound attenuating benefits may be derived by causing a previously split and recombined exhaust gas flow to pass through a turbulence generating zone.
The present invention departs from the prior art in contemplating combination concepts which uniquely integrate exhaust gas flow splitting and recombining with alternate compression and expansion which takes place while permitting increments of the exhaust gas flow to exit sequentially from a muffler. These combination concepts, hereinafter discussed, are significant in both a method and apparatus sense.
These individually significant aspects of the invention will now be described with respect to the method context of the invention, it being understood that each individual significant method aspect is associated with a counterpart apparatus aspect, also of independent significance.
A first method aspect of the invention resides in a method for attenuating sound levels of exhaust gas issuing from engine exhaust systems, which method comprises:
transmitting a flow of engine exhaust gas into muffler means;
splitting the exhaust gas flow into first and second, flow paths within the muffler means;
recombining exhaust gas from each of the first and second flow path within the muffler means by
alternately compressing and expanding the exhaust gas flow while concurrently
In a second, independently significant method aspect of the invention, the first method aspect is supplemented by the progressive constricting of exhaust gas flow in each of the first and second flow paths, with the exhaust gas in each of the first and second flow paths, during this progressive constricting, passing in heat dissapating relationship with heat transmitting external wall means of the muffler means. The recombining of exhaust gas flow from each of the first and second flow paths is effected with an abrupt constriction of the unified exhaust gas flow and the concurrent causing of the unified exhaust gas flow to abruptly undergo a transversely directed change in flow direction. Alternately opposite, transverse changes in flow direction are caused to occur in the exhaust gas flow concurrently with the alternate compressing and expansion of exhaust gas flow.
A third independently significant method aspect of the invention entails, following the recombining of exhaust gas flow from each of the first and second flow paths, the resplitting of the unified exhaust gas flow into third and fourth flow paths of generally equal length, with the first and second flow paths also being of generally equal length. Exhaust gas flow from each of these third and fourth flow paths is recombined by flowing gas from each of the third and fourth flow paths toward and into each other as generally mutually opposed gas flows to form a reunified exhaust gas flow.
A fourth independently significant method aspect of the invention entails a refinement of the third method aspect wherein gas flowing through each of the first, second, third and fourth flow paths is progressively constricted and caused to pass in heat dissapating relation with heat transmitting external wall means of the muffler means. In addition, unified exhaust gas flow obtained by recombining exhaust gas from each of the first and second flow paths is abruptly constricted and caused to abruptly undergo a transversely directed change in flow direction.
A fifth independently significant method aspect of the invention entails a refinement of the fourth method aspect wherein exhaust gas flow is caused to expand after the recombining of exhaust gas flowing from the first and second flow paths. In addition, exhaust gas is caused to undergo generally opposite, transverse changes in flow direction in conjunction with the alternate compressing and expansion of the reunified exhaust gas flow.
Having generally described the various independently significant aspects of the invention, a detailed description of a presently preferred form of the invention will be presented with respect to the appended drawings.